In radio communication systems, it is often desirable to improve the probability of detection of a communicated signal. For signals communicated using frequency modulation (FM), much attention has been paid to improving receiver sensitivity to communicated signals in the presence of noise. Receiver sensitivity can be improved by an approach known as noise threshold extension. Various techniques have been proposed for noise threshold demodulators. Among these techniques are the use of phase locked loops and frequency modulation feedback arrangements in the receiver. Such techniques reduce the influence of noise and undesired signals during the demoulation process. By extending the noise threshold, the receiver becomes more sensitive to weak signals thus increasing the probability of the detecting a communicated signal.
Noise affecting signals may arise from internal and external sources. Internal noise may be created through thermal energy generated during operation of circuitry used to process the signals. This type of internal noise is generally referred to as thermal noise. The impact of thermal noise on receiver sensitivity can be substantial when attempting to detect weak signals, particular those below the noise threshold of a receiver. When the input signal is sufficiently small, so as to be below the noise threshold, the operation of the demodulation process results in an increase in noise at the output. As a result, it becomes substantially more difficult to detect such signals.
In many situations, it is desirable to extended the range of certain transmissions made for signaling purposes. By improving receiver sensitivity, the effective range of a communicated signal is increased. However, thermal noise and other factors present an impediment to improved receiver sensitivity. Therefore, a new approach to enhancing signal detection for frequency modulated communications is needed.